1 files changed, 83 insertions, 0 deletions
diff --git a/main/src/addins/CSharpBinding/Util/TokenComparer.cs b/main/src/addins/CSharpBinding/Util/TokenComparer.cs
new file mode 100644
index 0000000000..2fe8d6f412
--- /dev/null
+++ b/main/src/addins/CSharpBinding/Util/TokenComparer.cs
@@ -0,0 +1,83 @@
+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.Globalization;
+using Microsoft.CodeAnalysis.CSharp.Extensions;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+
+namespace ICSharpCode.NRefactory6.CSharp
+{
+	internal class TokenComparer : IComparer<SyntaxToken>
+	{
+		private const string SystemNamespace = "System";
+
+		public static readonly IComparer<SyntaxToken> NormalInstance = new TokenComparer(specialCaseSystem: false);
+		public static readonly IComparer<SyntaxToken> SystemFirstInstance = new TokenComparer(specialCaseSystem: true);
+
+		private readonly bool _specialCaseSystem;
+
+		private TokenComparer(bool specialCaseSystem)
+		{
+			_specialCaseSystem = specialCaseSystem;
+		}
+
+		private static bool IsSystem(string s)
+		{
+			return s == SystemNamespace;
+		}
+
+		public int Compare(SyntaxToken x, SyntaxToken y)
+		{
+			if (_specialCaseSystem &&
+				x.GetPreviousToken(includeSkipped: true).IsKind(SyntaxKind.UsingKeyword, SyntaxKind.StaticKeyword) &&
+				y.GetPreviousToken(includeSkipped: true).IsKind(SyntaxKind.UsingKeyword, SyntaxKind.StaticKeyword))
+			{
+				var token1IsSystem = IsSystem(x.ValueText);
+				var token2IsSystem = IsSystem(y.ValueText);
+
+				if (token1IsSystem && !token2IsSystem)
+				{
+					return -1;
+				}
+				else if (!token1IsSystem && token2IsSystem)
+				{
+					return 1;
+				}
+			}
+
+			return CompareWorker(x, y);
+		}
+
+		private int CompareWorker(SyntaxToken x, SyntaxToken y)
+		{
+			if (x == y)
+			{
+				return 0;
+			}
+
+			// By using 'ValueText' we get the value that is normalized.  i.e.
+			// @class will be 'class', and unicode escapes will be converted
+			// to actual unicode.  This allows sorting to work properly across
+			// tokens that have different source representations, but which
+			// mean the same thing.
+			var string1 = x.ValueText;
+			var string2 = y.ValueText;
+
+			// First check in a case insensitive manner.  This will put 
+			// everything that starts with an 'a' or 'A' above everything
+			// that starts with a 'b' or 'B'.
+			var compare = CultureInfo.InvariantCulture.CompareInfo.Compare(string1, string2,
+				CompareOptions.IgnoreCase | CompareOptions.IgnoreNonSpace | CompareOptions.IgnoreWidth);
+			if (compare != 0)
+			{
+				return compare;
+			}
+
+			// Now, once we've grouped such that 'a' words and 'A' words are
+			// together, sort such that 'a' words come before 'A' words.
+			return CultureInfo.InvariantCulture.CompareInfo.Compare(string1, string2,
+				CompareOptions.IgnoreNonSpace | CompareOptions.IgnoreWidth);
+		}
+	}
+}